Patients with gyrate atrophy (GA) of the choroid and retina are examined systematically to confirm the diagnosis. Skin fibroblasts from affected patients and family members are grown in tissue culture and assayed for ornithine aminotransferase activity. The results are evaluated for correlation with the presence of homozygosity or heterozygosity for the disease trait. Each patient is given a trial of pyridoxine to see whether serum concentration of ornithine can be reduced; if so, the patient is classified as a "responder," and treatment with pyridoxine is continued. Nonresponder and responder and responder patients are then placed on a low-arginine, low- protein diet with supplemental amino acids and observed for arrest or improvement of the disease. If patients are not considered eligible for the diet, or if they appear unable to comply with the dietary regimen, we follow them to record the natural progression of the condition. Patients with other forms of retinal degeneration such as retinitis pigmentosa, fundus flavimaculatus, juvenile retinoschisis, and Bietti's crystalline dystrophy are also examined. The courses of their diseases are compared with those of GA patients.